This invention is generally related to predictions of casting defects and microstructures in castings, and in particular, to a methodology to simulate and predict the size and volume fraction of casting defects and microstructures in the castings without knowing the casting gating and riser design.
Aluminum castings are widely used in structural applications because of their high strength to weight ratio, good corrosion resistance, and relatively low raw material cost. Although it is cost competitive with other manufacturing methods, the casting process associated with aluminum alloys can introduce a substantial amount of defects, such as microporosity and oxides, into the material which significantly reduce fatigue and other mechanical properties.
Predicting the occurrence of such defects, as well as alloy and process dependent microstructures, prior to establishing a manufacturing process would be of significant value, as design and manufacturing alternatives could be explored and eventually optimized that would lead to improved reliability in the cast product.
Mathematical modeling of casting processes is now highly advanced, with commercial programs available to predict mold filling and solidification behavior for virtually any casting process. Software that predicts macro-scale thermal, pressure, and velocity distribution as well as macro defects such as trapped air and macro shrinkage porosity from mold filling and solidification is readily available, with the accuracy dependent upon the numerical methods and boundary conditions applied. However, the prediction of microporosity, oxides, and detailed microstructures is much less advanced and is very limited in commercial programs.
To predict casting defects and microstructure formed during mold filling and solidification processes accurately, the full mold geometry must be part of the model. The mold geometry and construction (e.g., locations, sizes of gates, runners, and risers, mold materials, part orientation in the mold during pouring and solidification, etc.) are important intellectual properties of foundries. Accordingly, foundries are reluctant to share this information.
Many customers purchase cast aluminum parts/systems from various suppliers. An accurate reliability analysis of those parts/systems becomes problematic because the casting defects and microstructure in those purchased parts/systems cannot be predicted with the existing approach.
Therefore, there is a need for a method of predicting casting defects and microstructure in cast aluminum parts when the details of the casting layout and gating/riser design as well as casting process parameters are not known.